Power Grid Reliability – Inside Energyhttp://insideenergy.org
Bringing energy reporting down to EarthWed, 14 Jun 2017 22:35:31 +0000en-US
hourly
1 https://wordpress.org/?v=5.4.1IE Questions: What Is Inertia? And What’s Its Role In Grid Reliability?http://insideenergy.org/2015/06/15/ie-questions-what-is-inertia-and-whats-its-role-in-reliability/
http://insideenergy.org/2015/06/15/ie-questions-what-is-inertia-and-whats-its-role-in-reliability/#commentsTue, 16 Jun 2015 00:27:54 +0000http://www.insideenergy.org/?p=2118This week’s question comes from one of our very own reporters, Leigh Paterson. On a recent trip, she experienced this:

Inside Energy producer Rebecca Jacobson and I visited a coal-fired power plant in eastern Wyoming. We wanted to find out why coal is so reliable and how switching away from it could impact our ability to keep electricity flowing. We started by visiting the plant’s coal stockpile. That part was fairly straightforward: Whenever you need more coal, just scoop up more from your gigantic pile. Then our tour guide took us inside the plant.

The control room at the Laramie River Station is dimly lit with high ceilings, ringed by several grids of computer screens. A guy on the phone was calling an order in for more coal. When we walked in with our camera, workers wearing Carhartts and blue jeans, faces illuminated by the large screens, joked nervously back and forth. As one guy walked me through the plant’s operations, using a touch screen with icons of little boilers and pulverizers, he dropped a lot of new vocabulary, including the concept of inertia. And the more I learned over the course of reporting this story, the more I realized that inertia is a huge factor in grid reliability – not just for coal-fired power plants, but for renewables and the electric grid as a whole.

Rebecca Jabobson / Inside Energy

Leigh Paterson in front of the array of screens in the control room at Laramie River Station, a coal-fired power plant in Wyoming.

So, what exactly is inertia? And what role does it play in electricity generation? Question one, we answer today. In an upcoming IE Questions, we’ll tackle why inertia is an essential part of of making sure electricity is there when you need it.

Inertia: A mechanical concept

Inertia is one of the most basic concepts of physics. Essentially, things that are moving will keep moving unless a force – like friction – causes them to stop. And things that are not moving will continue to not move unless a force – like a gust of wind – causes them to move. (Sound familiar? You may have learned about this in high school physics as Newton’s First Law of Motion.)

This concept is simple, but it’s not always easy to see.

Salem State University Assistant Professor of Physics, Anat Burger, (who, full disclosure, also happens to be a good friend of mine) put it this way:

The reason why the concept of inertia was not immediately obvious to everyone before Newton is because our world is filled with sources of friction that act to resist motion. For example, if you give a box a push, it will not continue moving at a constant speed, it will very quickly come to a stop. That is because of the friction acting between the box and the floor. In order to see inertia at work, we need systems that have very low friction, such as in outer space.

Inertia is often best understood through examples, like this one of why a giraffe needs to wear a seat-belt*:

Jordan Wirfs-Brock / Inside Energy

Because of her height, a giraffe still gets a pretty severe case of whiplash, but without a seat-belt her whole body would have been thrown out of the car.

A slightly less intuitive example is what happens when you – or a llama – launches a projectile from a moving vehicle:

Jordan Wirfs-Brock / Inside Energy

The projectile – er, flying blob of llama saliva – has forward motion when it leaves the car, so it continues moving in that direction and lands right on top of the llama’s head.

Rotating objects also exhibit inertia. Ever wonder what happens if a hamster on a wheel suddenly stops running?

Jordan Wirfs-Brock / Inside Energy

The wheel keeps moving, and the hamster goes right along with it – until friction slows them both down.

So what about power plants? Do they have inertia?

Yes.

Let’s start with a coal-fired power plant: Coal is burned, which produces steam, which spins a turbine, which generates electricity, which is is connected straight to the electric grid. The plant works with the help of a heavy, rotating mass that has inertia. If you suddenly stop burning coal, the turbine will keep spinning – for a while, at least.

In fact, any power plant with moving parts has inertia. Take a hydroelectric power plant or dam: It works the same way as a coal-fired plant, only instead of steam, water turns the turbine. If you magically removed the water and disconnected the turbine from the generator, the turbine would keep spinning until friction stopped it.

To put it another way, if our hamster on a wheel were generating electricity – although you’d need an army of them to power a lightbulb – you could exchange the hamster for a gerbil and it would work the same way. Just like you could exchange coal for natural gas or for water and your power plant would work in much the same way.

Wind farms also have rotational inertia. If the wind turbines are spinning – depending on the size of the turbine, the tips of the blades can move at speeds of 180 miles per hour – and the wind suddenly stops, the turbines will keep moving until friction, and the conversion of rotational energy to electricity, slows them down.

Jordan Wirfs-Brock / Inside Energy

The pinwheel keeps moving, even after the elephant stops blowing.

What about solar power? This is the key issue with inertia and renewable: Solar panels, or photovoltaic cells, don’t have any moving parts, so they don’t have any mechanical inertia. When the sun stops shining, because clouds roll in or there’s an eclipse, the solar panels stop generating electricity immediately.

But the reverse is also true: When the clouds roll away, solar panels immediately start generating electricity at full capacity. Not so for those power plants with big, heavy, spinning parts: It takes some time for the turbines in a coal-fired power plant to get back up to full speed.

When we hook individual power sources – nuclear plants, wind farms, solar gardens, natural gas plants – up to the electric grid, the reliability of the entire system depends on the concept of inertia. To understand why, we’ll need to go beyond spinning hamsters and frustrated llamas and dive into something called “frequency response,” and even revisit the historic AC/DC battle. For that, check out part two of our investigation into inertia and the electric grid.

*Note: The animated gifs were not made using a physics simulator. Their motion represents a rough approximation of Newtonian physics.

Have an idea for an energy topic that could be fun in the classroom? Submit it below.

The coal stockpile at Laramie River Station is so big that you can’t really see beyond it. It is similar to standing on the beach and looking out over the ocean, except this is an ocean of coal. The 35 acres of coal piled up next to this base load power plant is enough to produce electricity for about one month. Our entire electric grid was basically constructed to send this sort of coal-fired power out over transmission lines to our homes and businesses long ago. Coal as a source of power is predictable, easy to store, and well understood. Renewables and even natural gas share few of these characteristics and some see that as a huge problem.

As the Environmental Protection Agency puts the finishing touches on the Clean Power Plan, its proposal to cut carbon dioxide emissions, warnings that the transition from coal to renewables and natural gas will impact grid reliability are getting louder.

Representative Ed Whitfield (R-KY), the Chairman of the Energy and Power Subcommittee, referred to an analysis by grid operator PJM Interconnection, when he said: “The president’s plan could cause 50 million American homes to go dark – you cannot just shut down the nation’s coal plants and still expect the lights to come on.”

In April, the Wall Street Journal ran an editorial with the headline: “The State Electricity Revolt,” suggesting that states boycott the Clean Power Plan:

“Virtually everyone who understands the electric grid, from state utility commissions to the regional transmission operators, warns that the EPA’s ambitions threaten reliability. These apolitical organizations think brownouts or cascading blackouts are possible.”

The North American Electric Reliability Corporation (NERC) is the non-profit tasked with ensuring grid reliability. NERC released a report in November, confirming these concerns… sort of. It lists challenges like finding replacement generation for the coal-fired power plants that could go offline and challenges in the building enough infrastructure to support new sources of electricity. But the report did not predict brownouts or cascading blackouts. John Moura, Director of Reliability Assessment at NERC and one of the authors of the report, boiled down its overarching theme in a conversation with Inside Energy:

“There is a level of risk in having every utility going down that same path at the same time.”

But here’s the thing: Under the proposed plan, coal isn’t necessarily going to disappear. States are able to choose how to comply through measures like retrofitting coal-fired power plants, energy efficiencies and adding more renewables.

“Well, can we have a reliable grid without the level of coal fired generation that we have right now? I think the answer is a resounding, yes, of course we can,” Cheryl Roberto of the Environmental Defense Fund said.

We have been moving towards other fuel sources for awhile. According to the U.S. Energy Information Administration, the total amount of coal-fired generation has decreased slightly since the 1990s, while natural gas capacity has been increasing since the 1980s. In 2014, one coal-fired power plant went online in the US and 41 were retired. The same number of natural gas facilities went offline but 82 were added. But renewables win with over 300 new units in 2014, with only a handful of retirements.

A good place to check out that trend? Southern California. At around 34%, San Diego Gas and Electric has some of the highest renewable integration in the country. The rest of its power comes mostly from natural gas. SDG&E got rid of its small amount of coal-fired generation a few years ago. Over the past decade, SDG&E’s reliability statistics have gone up and down but overall, haven’t changed much.

Which is not to say that running off so much natural gas, wind, and solar is easy.

“The challenges are many,” Dan Baerman, Director of Origination and Portfolio Design at SDG&E said, “One of the big ones that concerns us is its impact on rates for our customers. We try to minimize the impact as much as possible by getting renewables that are economical.”

And then there is this:

“Wind and solar are intermittent resources so … it makes it difficult to maintain grid reliability,” Baerman said.

One of their solutions? Peaker plants. These small, natural gas-fired facilities can be powered up in minutes in times of high demand. SDG&E currently operates 24 of these units which Baerman described as “essentially air craft engines coupled with generators to make electricity.”

Alison St. John of KPBS reported on a decision by the California Public Utilities Commission earlier this month to approve a plan to build a peaker plant in Carlsbad California that will provide extra power to SGD&E customers.

“It gives us that critical insurance to get through the next 5, 10, 15 years to when we can really be confident that we have a grid that can work,” CPUC Commissioner Mike Florio said.

Here’s what he is trying to avoid:

“The absolutely worst thing that could happen if we have reliability problem and the whole world points and says look what happened to California, this clean energy stuff doesn’t work.”